Damage

Damage is a measurement of how harmful an attack is to a character.
When a character takes Damage, it is subtracted from his or her Hit Points.
Damage will cause death when a character's hit points reach 0.

^aFallout: New Vegas features a few weapons that completely ignore DR, even if few enemies actually have DR.^b Damage done to the player in V.A.T.S. is reduced by 90%.^c Damage done to the player in V.A.T.S. is reduced by 25%. Melee/unarmed damage done by the player is doubled.

Damage dealt through radioactive sources such as certain weapons or environments. c

Energy

Damage dealt by lasers, fire, electricity, cold, and a variety of other sources, including weapons which inflict more than one damage type, such as plasma.

Poison

Damage dealt primarily by toxins, typically from a bug, but also including some exotic weaponry.

^a Not shown in the games that use it, Electrical damage is only caused by alien blaster, YK32 pulse pistol, and YK42B pulse rifle.^bFallout 3 and Fallout: New Vegas use "energy" damage to label the residual effect off the Tesla cannon, though it has the appearance of electricity sparking.^c All Fallout games contain environmental radiation damage of some variant. The table is representative of radioactive damage dealt by weapons like the gamma gun.^d Exists in the game files, but is not used anywhere.